fix browserify cannot find module when use "npminstall" install packages

[allenm]

fix browserify cannot find "is-buffer" pacakge from "core-util-is" when use "npminstall" install packages.

You can use this repo ( browserify-link-bug ) to reproduce this bug.

[allenm]

@substack npminstall is awesome , it's very fast . Wish you fix this bug ASAP.

[martinheidegger]

@allenm It is easier to review and understand the problem with a test case that validates it.